[llvm] AArch64/GlobalISel: Mark the LR def of the Mach-O TLS call dead (PR #227234)

[via llvm-commits]

llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: Matt Arsenault (arsenm)

<details>
<summary>Changes</summary>

The ordinary call path already does this, and the SelectionDAG emitter
marks unused implicit physreg defs dead for free. Without it the dead
flag needs to be reinferred later.

Co-Authored-By: Claude Opus 5 <noreply@<!-- -->anthropic.com>

---
Full diff: https://github.com/llvm/llvm-project/pull/227234.diff


2 Files Affected:

- (modified) llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp (+1) 
- (added) llvm/test/CodeGen/AArch64/GlobalISel/select-tls-macho.ll (+30) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
index 309dbd0def387..22c0e3a3a462d 100644
--- a/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
+++ b/llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp
@@ -3920,6 +3920,7 @@ bool AArch64InstructionSelector::selectTLSGlobalValueMachO(
   }
 
   MIB.buildInstr(Opcode, {}, {Load})
+      .setOperandDead(1) // implicit-def $lr
       .addUse(AArch64::X0, RegState::Implicit)
       .addDef(AArch64::X0, RegState::Implicit)
       .addRegMask(TRI.getTLSCallPreservedMask());
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/select-tls-macho.ll b/llvm/test/CodeGen/AArch64/GlobalISel/select-tls-macho.ll
new file mode 100644
index 0000000000000..0586ac29f4105
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/select-tls-macho.ll
@@ -0,0 +1,30 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -mtriple=arm64-apple-macosx -global-isel -O0 -stop-after=instruction-select < %s | FileCheck %s
+
+ at tls_var = external thread_local global i32
+
+define ptr @tls_addr() {
+  ; CHECK-LABEL: name: tls_addr
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK-NEXT:   [[LOADgot:%[0-9]+]]:gpr64common = LOADgot target-flags(aarch64-tls) @tls_var
+  ; CHECK-NEXT:   [[LDRXui:%[0-9]+]]:gpr64common = LDRXui [[LOADgot]], 0
+  ; CHECK-NEXT:   $x0 = COPY [[LOADgot]]
+  ; CHECK-NEXT:   BLR [[LDRXui]], csr_darwin_aarch64_tls, implicit-def dead $lr, implicit $sp, implicit $x0, implicit-def $x0
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr64 = COPY $x0
+  ; CHECK-NEXT:   $x0 = COPY [[COPY]]
+  ; CHECK-NEXT:   RET_ReallyLR implicit $x0
+  ret ptr @tls_var
+}
+
+define ptr @tls_addr_ptrauth() "ptrauth-calls" {
+  ; CHECK-LABEL: name: tls_addr_ptrauth
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK-NEXT:   [[LOADgot:%[0-9]+]]:gpr64common = LOADgot target-flags(aarch64-tls) @tls_var
+  ; CHECK-NEXT:   [[LDRXui:%[0-9]+]]:gpr64common = LDRXui [[LOADgot]], 0
+  ; CHECK-NEXT:   $x0 = COPY [[LOADgot]]
+  ; CHECK-NEXT:   BLRAAZ [[LDRXui]], csr_darwin_aarch64_tls, implicit-def dead $lr, implicit $sp, implicit $x0, implicit-def $x0
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr64 = COPY $x0
+  ; CHECK-NEXT:   $x0 = COPY [[COPY]]
+  ; CHECK-NEXT:   RET_ReallyLR implicit $x0
+  ret ptr @tls_var
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/227234